Process for improving heat transfer efficiency and improved heat transfer system

ABSTRACT

The instant disclosure teaches a process for improving heat transfer efficiency and an improved heat exchange system utilizing an improved highly corrosion resistant enhanced metal tubing consisting essentially of from 0.5 to 4.0 percent iron, balance essentially copper.

United States Patent 1191 Ford Feb. 5, 1974 PROCESS FOR IMPROVING HEAT [56] References Cited TRANSFER EFFICIENCY AND IMPROVED UNITED STATES PATENTS HEAT TRANSFER SYSTEM 3,154,141 10/1964 I-Iuet 165/133 [75] Inventor: James A, Ford, North Haven Conn 3,530,923 9/1970 Mattem 165/146 3,612,175 10/1971 Ford et al. 165/179 [73] Assignee: Olin Corporation, New Haven,

Conn Primary Examiner-Charles Sukalo [22] Filed; Apr, 23, 1971 Attorney, Agent, or Firm-Robert H. Bachman 21 l. N .1 136,726 1 App 57 ABSTRACT f q Apphcanon Data The instant disclosure teaches a process for improving 1 commuanon-m-pal't of 822,686 May heat transfer efi'iciency and an improved heat ex- 1969' change system utilizing an improved highly corrosion resistant enhanced metal tubing consisting essentially [52] US. Cl. 165/1, 165/133 of from 05 to 40 percent iron balance essentially [51] Int. Cl F28f 13/18 [58] Field of Search 165/146, 179, 172, 133

8 Claims, 2 Drawing Figures O 1 o 0 o m 0 0114 0 03 PAIENIEB FEB 5 I974 A A A 5 A A AA FIG-2 JAMES A. FORD INVENTOR aal/1&4.

I ATTORNEY PROCESS FOR IMPROVING HEAT TRANSFER EFFICIENCY AND IMPROVED I-IEAT TRANSFER SYSTEM CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of copending application Ser. No. 822,686, by James A. Ford for Corrosion Resistant Metal Tubing, filed May 7, 1969.

BACKGROUND OF THE INVENTION The production of potable water from saline water requires extensive quantities of heat transfer surface in the form of condenser tubing. Estimates have variously placed the capital investment involved with the heat exchanger surface in desalting plants at as much as 50 percent of the total.

Accordingly, it becomes extremely pertinent in the continuing efforts to reduce the cost of potable water that the cost of the heat transfer surface be reduced. It is known in the art that corrugated tubing or surface enhancement provides improved heat transfer efficiency as compared to a plain cylindrical tube.

It is highly desirable, however, to provide still further improvement in this art.

Accordingly, it is a principal object of the present invention to provide a process for improving heat transfer efficiency and an improved heat exchange system.

. vention will appear from the ensuing specification.

SUMMARY OF THE INVENTION In accordance with the present invention it has now been found that the foregoing objects and advantages may be readily achieved and an improved process and heat exchange system provided. The process of the present invention comprises: providing an enhanced hollow tube consisting essentially of from 0.5 to 4.0 percent iron, balance essentially copper, said tubing having an enhanced central section, a relatively smooth entrance end and a relatively smooth exit end; affixing said entrance and exit ends to two tube sheets; passing a first fluid through said tubing; and contacting the external surface of said tubing with a second fluid in heat transfer relationship with the first fluid.

The improved heat transfer system comprises: providing an enhanced metal tubing having an enhanced central section, a relatively smooth entrance end and a relatively smooth exit end, said tubing consisting essentially of from 0.5 to 4.0 percent iron, balance essentially copper; a first entrance tube sheet affixed to the entrance end of the enhanced tubing; a second exit tube sheet affixed to the exit end of the enhanced tubing; a first fluid passing through the enhanced tubing; and a second fluid in contact with the external walls of the enhanced tubing in heat exchange relationship with the first fluid.

In accordance with the present invention it has been found that the foregoing process and heat transfer system achieves a surprisingly high heat exchange efficiency. This surprising heat exchange efficiency could not be anticipated, even in view of the high corrosion resistance of the alloys which are utilized for the enhanced tubing.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. 1 shows a side view of a portion of enhanced metal tubing of the corrugated type utilized in the present invention; and

FIG. 2 shows a side view of a portion of enhanced metal tubing of the knurled type utilized in the present invention.

DETAILED DESCRIPTION The enhanced tubing which is utilized in the present invention has at least one surface thereof enhanced, preferably the outer surface. A variety of processes may be utilized to provide the enhanced surface, such as by corrugating, texturing, dimpling inwardly or outwardly, or knurling.

Thus, the tubing should have a series of protrusions or protrusion-like shapes which serve to thin the film of condensing fluid and thereby increase the condensing film heat transfer coefficient or decrease its heat transfer resistance.

In accordance with the present invention, a surprising improvement in heat exchange efficiency is obtained. The particular alloys utilized are altered from a smooth, relatively flat surface tube into a tube having an irregular surface. The thus altered tubing is utilized in the process and heat transfer system of the present invention to obtain an unexpected improvement,-as will be apparent from the ensuing specification.

An additional advantage of external surface enhancement is that concurrently the internal waterside or cooling side coefficient is surprisingly increased and the heat transfer resistance decreased. This is caused by a combination of factors which may work together or separately. In the first place, surface enhancement decreases the stagnant layer thickness on the inside of the tube due to associated surface roughness. In the second place, surface enhancement increases heat flux due to increased condensing film coefficient and decreasing heat transfer resistance on the outside surface. The level of the improvement which is obtained, however, is believed to be surprising.

It should be understood that in accordance with the present invention it is unnecessary to enhance both the inside and outside surfaces. It is only required in accordance with the present invention that at least one surface be enhanced. For example, in the knurling embodiment a surprising improvement is obtained even though the enhancement is on the outside or inside surface. Inside or outside knurled tube may be readily obtained by welded tube techniques by knurling the desired surface of the metal strip prior to welding.

In accordance with the present invention a particularly preferred metal tubing is corrugated metal tubing. The corrugated tubing may be obtained by any method known in the art. A particularly preferred method and apparatus for obtaining the corrugated tubing is shown in US. Pat. No. 3,578,075 by Joseph Winter. In accordance with the teaching of the foregoing patent, corrugated tubing is produced by an apparatus characterized by having an inner frame moveably mounted on an outer frame, with a die rotatably mounted on the inner frame. The die has an annular opening through which passes the tube to be corrugated and shaped die members projecting into the annular opening. The pitch and depth of the spirals or corrugations can be adjusted and controlled over a wide range of configurations.

The corrugated tubing utilized in accordance with the present invention should have a plurality of lands and grooves extending along the circumference thereof in the conventional manner.

Enhanced tubing would be expected to have increased heat transfer capacity due to the increased surface area per unit length of tube and increased turbulence generated both inside and outside the tube. As indicated hereinabove, however, the enhanced tubing of the present invention achieves a surprisingly high level of heat transfer efficiency coupled with high corrosion resistance. It is particularly surprising that so high a level of heat transfer efficiency is obtained even with respect to the preferred corrugated tubing produced in accordance with the teaching of the aforesaid U.S. Pat. No. 3,578,075 wherein the surface area per unit length is not increased.

In the drawings which form a part of the present specification, FIG. I shows a side view of a portion of representative corrugated tubing used in the present invention produced in accordance with the teaching of the aforesaid U.S. Pat. No. 3,578,075. In FIG. 1, reference numeral 1 shows the plain uncorrugated end and reference numeral 2 shows the corrugated portion.

FIG. 2 shows a side view of a portion of representative knurled tubing which may be used in the present invention. In FIG. 2, reference numeral 3 shows the knurled portion and reference numeral 4 shows the plain end.

The alloy utilized in the tubing of the present invention, is a copper base alloy containing from 0.5 to 4.0 percent iron and preferably from 1 to 3 percent iron. It is preferred in accordance with the present invention to utilize phosphorus as an additive in an amount up to 0.5 percent and preferably from 0.15 to 0.04 percent.

Naturally, other additives may be provided such as the following materials in amounts from 0.01 to l percent by weight: vanadium, chromium, molybdenum, silicon, tin, titanium, aluminum, arsenic, antimony, columbium, cobalt and tantalum. In addition to the foregoing, the copper base alloy of the present invention may contain zinc in an amount up to 0.3 percent and lead in an amount up to 0.05 percent. Other less preferred additives which may be tolerated include relatively small amounts, i.e., up to about 0.01 percent, of manganese and nickel.

The copper tubing of the present invention should have a wall thickness offrom 0.010 inch to 1.0 inch and an outside diameter of from 0.25 inch to 10.5 inch.

In use, normally a section of the tubing is left plain as shown in the drawings to provide a plain undistorted tube wall at each end of the tubing as a locus for sealing into a tube sheet. A multitude of tubes are conventionally attached to tube sheets which separate the heat transfer media on the outside from the heat transfer media on the inside of the tubes. The tubes are normally sealed at the point between the heat exchange tubes and the tube sheet by rolling in the tubes or by welding or by brazing.

The present invention will be more readily apparent from a consideration of the following illustrative examples.

EXAMPLE I This example utilizes a copper base alloy having the following composition: iron, 2.3 percent; phosphorus, 0.025 percent; copper, essentially balance. Seam welded tubing was prepared from the foregoing alloy having a total length of 42 inches. Tubing had a one inch OD. and a wall thickness of 0.049 inch. Some of the tubing was formed into corrugated tubing having a plurality of lands and grooves extending along the circumference thereof. The corrugated tubing exhibited no change in weight per unit length, i.e., the corrugated tubing had no greater surface area in one foot. The convoluted section of the tube was about 33 inches long. The corrugated tubing had about a 4-5 inch plain section on either end.

The plain tubing and the corrugated tubing were both tested in the same manner. A single tube, horizontal calorimeter was used operating on filmwise condensation of steam at approximately 240F using tap water as cooling water on the interior of the tube. The inlet temperature of the tap water was about 40F. The heat transfer characteristics of the tubes were determined over a range of water velocity. The values in the table set out below are for a velocity of 6 feet per second. The heat transfer coefficient was determined by measuring cooling water flow in mass rate and measuring inlet and outlet temperature of cooling water to determine heat flux. This was related to overall heat transfer coefficient, p.,,, using the equation Q [.(A AT wherein Q heat flux in BTU per hour;

A heat transfer area of the outside surface of the tube; and

AT= log mean temperature difference for condensing steam cooling water system. The results are shown in Table I below. The heat transfer coefficients are expressed in the followung units: BTU/- hour square foot F.

TABLE I Plain Corrugated Percent Tube Tube Enhancement Overall heat transfer coefficient 670 I380 106 Waterside coefficient 1910 5500 288 -Steamside coefficient I080 1960 81.5

EXAMPLE II This example represents a comparison between the corrugated tubing of Example I, tubing A, and corrugated tubing of a different alloy, tubing B. Corrugated tubing B was prepared in the same manner as corrugated tubing A except that its composition was as follows: nickel, 10 percent; iron, 1.5 percent, copper, essentially balance. The results are shown in Table ll, below.

TABLE II Corrugated Percent Corrugated Percent Tubing A Enhance Tubing B Enhancement ment Over Over Plain Plain Tubing A Tubing B Overall heat 1 transfer coefficient I380 106 1070 59.7

Waterside coefficient 5500 288 5210 273 Steamside coefficient 1960 81.5 1410 30.6

It is apparent that the Alloy A corrugated tubing is considerably superior to the Alloy B corrugated tubing, both of which are better than the respective plain tubing. This is due in part to the superior thermal conductivity of the Alloy A (151 BTU/hour square foot F/foot) as compared to Alloy B (26 BTU/hour square foot F/foot). However, as an examination of the data in Table 11 shows, there is a significantly greater enhancement of the steamside coefficient for Alloy A. This is completely unexpected since the geometry of the tubes is constant. The differences in thermal conductivity would normally be expected to exert a small difference in heat transfer coefficient, but certainly not of the order of magnitude experienced above.

EXAMPLE III In this example a copper base alloy was utilized having the following composition: iron, 2.3 percent; phosphorus, 0.025 percent; zinc, 0.15 percent; copper, essentially balance. Seam welded tubing was prepared from the foregoing alloy with tubing C having the inside surface only knurled, and tubings D and E having the outside surface only knurled. Tubing F represents plain, unknurled tubing. The knurling was accomplished by passing the strip through patterned rolls prior to scam welding. The tubing had a one inch OD. and a wall thickness of 0.625 inch.

All tubes were tested in a manner after Example 1, except that values were determined for a water velocity of 2 feet per second and four feet per second as well as six feet per second. The results are shown in Table III below. The results clearly show a surprising improvement with inside as well as outside knurled tubing.

TABLE 1]] Tube C Tube D Tube E Tube F Overall heat transfer coefficient at 2 fps 633 581 547 450 :11. 4 fps 803 800 766 600 a! 6 fps 892 931 900 680 Waterside coefficient at 2 fps 127| 904 813 660 at4fps 2213 1575 1416 1035 at 6 fps 3061 2178 i958 1300 Steamside coefficient 1326 1739 1786 1484 This invention may be embodied in other forms or carried out in other ways without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered as in all respects illustrative and not restrictive, the cope of the invention being indicated by the appended claims, and all changes which come within the meaning and range of equivalency are intended to be embraced therein.

What is claimed is:

1. A process which comprises:

A. providing an enhanced hollow metal tubing having a wall thickness of from 0.010 inch to 1.0 inch consisting essentially of from 0.5 to 4.0 percent iron, balance essentially copper, said tubing having an enhanced central section, a relatively smooth entrance end and a relatively smooth exit end, said enhanced central section having an irregular surface with a series of protrusions thereon;

B. passing a first fluid through said tubing; and

C. contacting the external surface of said tubing with a second fluid in heat transfer relationship with the first fluid, thereby providing improved heat transfer efficiency and high corrosion resistance.

2. A process according to claim 1 wherein said tubing is corrugated.

3. A process according to claim 2 wherein said tubing is spirally corrugated and exhibits substantially no change in weight per unit length as uncorrugated tubing of the same composition.

4. A process according to claim 1 wherein said tubing is knurled.

5. A process according to claim 1 wherein said tubing contains phosphorus in an amount from 0.015 to 0.04

percent. I

6. A process according to claim 5 wherein said tubing includes a material selected from the group consisting of the following elements in an amount from 0.01 to 1.0 percent by weight each: vanadium, chromium, molybdenum, silicon, tin, titanium, aluminum, arsenic, antimony, columbium, cobalt, tantalum and mixtures thereof.

7. A process according to claim 5 wherein said tubing includes zinc in an amount up. to 0.30 percent.

8. A process according to claim 1 wherein said tubing is welded tubing. 

2. A process according to claim 1 wherein said tubing is corrugated.
 3. A process according to claim 2 wherein said tubing is spirally corrugated and exhibits substantially no change in weight per unit length as uncorrugated tubing of the same composition.
 4. A process according to claim 1 wherein said tubing is knurled.
 5. A process according to claim 1 wherein said tubing contains phosphorus in an amount from 0.015 to 0.04 percent.
 6. A process according to claim 5 wherein said tubing includes a material selected from the group consisting of the following elements in an amount from 0.01 to 1.0 percent by weight each: vanadium, chromium, molybdenum, silicon, tin, titanium, aluminum, arsenic, antimony, columbium, cobalt, tantalum and mixtures thereof.
 7. A process according to claim 5 wherein said tubing includes zinc in an amount up to 0.30 percent.
 8. A process according to claim 1 wherein said tubing is welded tubing. 